linux-kernel - Reason for playing games with vector number on x86-64 interrupt handling

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:	Sun, 3 Feb 2013 21:33:18 +0200
From:	Ilya Lesokhin <ilya.lesokhin@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Reason for playing games with vector number on x86-64 interrupt handling

Hi,

I have a question related to interrupt handling on x86-64.

entry_64.s cains the following code:
     pushq_cfi $(~vector+0x80)       /* Note: always in signed byte range */
and later
     addq $-0x80,(%rsp)              /* Adjust vector to [-256,-1] range *
and then finally in irq.c
      unsigned vector = ~regs->orig_ax;

if I'm not mistaken regs->orig_ax contains ((~vector+0x80) -0x80) =
~vector and applying ~ again gives vector.

I was wondering, what is the reason for all those games with vector?
why not just push vector in the begging and save later instructions?

Please CC me in your answers.
Thanks,
Ilya
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/